The present invention relates to an apparatus for effectively photosynthesizing photosynthetic substances such as algae typified by chlorella or spirolina, photosynthetic bacteria or artificial photosynthetic substances such as callus.
Photosynthetic apparatuses heretofore proposed include an apparatus for culturing chlorella (unicellular microorganism containing chlorophyl). Difficulty experienced in culturing chlorella is that illumination with intensities higher than a certain level destructs the chlorophyl and produces a toxin (phaeophorbite) while illumination with intensities lower than a certain level fails to cause photosynthesis altogether. It is therefore a primary requisite for effective photosynthesis that all the cells containing photosynthetic substances be supplied with constant light of an even distribution. Generally, organisms in a swarm increase not only their multiplying ability per unit volume but their resistance to other funge. The culturing efficiency, therefore, grows poor unless a predetermined light radiating area per one liter of culture medium is ensured. With this in view, it has been customary to promote the transmission of light by reducing the number of photosynthetic substances (individuals). This involves an inconsistency, however, because an increase in the number of individuals lowers the transmissibility to light and, therefore, requires collection of the individuals, but the resulting decrease in the number of individuals weakens the resistance to the funge. Another drawback hitherto encountered is that the light intensity is excessively high for the individuals near a light source but is insufficient for those remote from the light source and, additionally, the light is absorbed by water to have its wavelength component varied. An ideal situation is, therefore, that photosynthetic substances be passed through a very narrow clearance while a predetermined intensity of light is directed perpendicular to the clearance. Then, sufficient light will be evenly applied to all the cells containing photosynthetic substances with a minimum of attenuation and without any change in its wavelength component. A photosynthetic apparatus presently in use includes a number of fluorescent lamps arranged in a reaction bath (e.g. chlorella culturing bath) and causes photosynthetic substances to flow through the gaps between the lamps. However, the use of fluorescent lamps renders the apparatus bulky, increases power consumption and requires an awkward measure against heat generation by the lamps. Moreover, fluorescent lamps generally have peaks at specific wavelengths and those having a peak in their green component, which is harmful for chlorophyl, are unsuitable for photosynthesis. Apparently, sunlight or like natural light is most adequate for culturing chlorella and the like.
While the even supply of a sufficient amount of carbon dioxide (CO.sub.2) all over the reaction bath is essential in attempting efficient photosynthesis, it has been quite difficult so far to fulfill such a condition.
Additionally, no effective means has been proposed for preventing contamination by the dead part of a photosynthetic substance or the like which tends to accumulate in various sections of a reaction bath.
In culturing chlorella, for example, one liter of culture medium extends over an area of 1 m.sup.2 when spread to a thickness of 1 mm. Meanwhile, when the culture medium is laid on a 1 m.sup.2 plane light source to a thickness of 1 mm, the intensity of the light source being assumed to be 1000 lx, the intensity after the light has passed through the 1 mm thick culture medium is reduced to about 30 lx in the case of a high density chlorella culture medium for enhancing the multiplying ability. Thus, hardly any light is allowed to reach chlorella located opposite to the plane light source. Although such a problem may be solved if plane light sources are located at both sides of the 1 mm thick culture medium, such results in generation of a significant amount of heat when the light sources comprise fluorescent lamps, as has been the case with conventional apparatuses.
Air is blown into the chlorella culturing bath from below in order to cause upwardly directed bubbling within the bath. Carbon dioxide (CO.sub.2) contained in the air which is the source of bubbling contributes to photosynthesis of chlorella, while oxygen (O.sub.2) resulting from the photosynthesis is discharged from the top of the bath. This promotes effective photosynthesis of chlorella.
The bubbling also serves to effectively diffuse and transmit light which is radiated by the photoradiators, and to agitate the cells from distributing the light to all the cells in the bath.
Furthermore, the bubbling keeps the surfaces of the photoradiators clear by exchanging gas, i.e. charging CO.sub.2 and discharging O.sub.2, preventing chlorella from being precipitated in a lower portion of the bath, and removing cells which deposit on the surfaces of the photoradiators. Thus it is a precondition in practicing the present invention that the apparatus be used in a vertical or upright position; using it in a horizontal position would not allow the bubbling to flow smoothly.
In accordance with the present invention, the distance between the photoradiators is selected to cope with the fact that mucilage coming out from the chlorella cells develops bubbles and these bubbles combine to form larger bubbles which tend to block the flow of the bubbling.
As described above, the present invention provides a chlorella culturing apparatus which uses bubbling. Another characteristic feature of the present invention is the instrumentation for solving problems which stem from generation of heat. that is, a light source is implemented by light which is guided by optical fibers, and light from the light source is distributed in an even intensity and an optimum quantity to all the cells in the bath. In detail, where 1 liter of culture fluid is poured onto a surface of 1 mm.sup.2, it spreads to a depth of 1 mm. When light with a luminous intensity of 1,000 lx is projected onto the 1 mm deep culture fluid, the intensity is reduced to as low as 30 lx after the transmission of the light through the fluid; photosynthesis is almost impossible at such a low intensity. Fluorescent lamps used to implement a 1,000 lx planar light source would generate excessive heat to obstruct effective chlorella culturing and, in addition, bring about the need for a special device for removing the heat, thereby increasing the cost and size of the apparatus. Bubbling in accordance with the present invention enhances diffusion and transmission of light through the culture fluid so that sufficient light is supplied to the whole chlorella to promote effective chlorella culturing.
Another advantage of the present invention is that since the photoradiators are individually provided with a triangular, rectangular, hexagonal, circular and other cross-sections, they can always be held in the same relationship, enabling the apparatus to be scaled up or down with ease.
An apparatus for photosynthesis embodying the present invention includes a photosynthetic reaction bath and a plurality of tubular photoradiators arranged upright in the reaction bath in parallel with each other. The reaction bath is communicated to a source of CO.sub.2 -containing air supply. A circulation means is provided for circulating in the reaction bath the CO.sub.2 -containing air which is fed from the conduit into the reaction bath.
In accordance with the present invention, a photosynthetic reaction bath has thereinside a number of photoradiators in the form of narrow upright tubes. A baffle plate is disposed below the photoradiators and is formed with a number of apertures therethrough in a predetermined area thereof which may be a radially central area or a generally annular peripheral area. CO.sub.2 -containing air is fed into the reaction bath through the apertures in the baffle plate to circulate along a predetermined path inside the reaction bath due to the remaining non-apertured part of the baffle plate. The function of the baffle plate may be performed by plugging which blocks the passage of the air through the spacings between the lower ends of the adjacent photoradiators in the predetermined area. The circulation of the air may be caused more positively along a variable path by a rotor which is positioned below the photoradiators and rotatable by ejecting the air while supplying it to the interior of the reaction bath. The rotor is cushioned and rotatably supported by the air ejected therefrom during operation.